Patent GB-416002-A (GB)
Title: Improvements in or relating to sewing machines
IPC: D05B15/04
Filed: 1933-02-02
Abstract: 416,002. Sewing-machines. BRITISH UNITED SHOE MACHINERY CO., Ltd., RICKS, F., GOULDBOURN, J., and ELLIOTT, H. E., Belgrave Road, Leicester. Feb. 2, 1933, Nos. 3176 and 10912. [Class 112.] The tendency of the shuttle thread to impose an undue strain on the needle thread and cause reeving of the two threads round each other in boot-sole sewing- machines of the kind described in Specifications 392,947 and 410,463, is avoided by providing means for slackening the tension of the shuttle thread. The invention is shown as applied to the lockstitch boot sole sewing machines described in the above Specifications. The bobbin case 3, Fig. 3, is held from complete rotation with the shuttle case 1, but is free to vibrate slightly to and fro, by a relatively fixed ridge engaging loosely in a V-shaped groove as described in Specification 392,947. It has a nose 5 and a hole 7 for the shuttle thread. This hole is spaced roughly about half way between the axis of the bobbin case and the nose 5. The amount of thread pulled off will therefore be fairly constant in spite of the vibrations of the thread exit and the setting of the stitch locks will be more uniform. The nose 5 prevents the shuttle thread, if it becomes unduly slack, from bending so far back that it is liable to be caught by the beak 9 of the rotating shuttle. The thread exit hole 7 is so positioned that it lies at the lower side of the bobbin case. The thread passes through an adjustable tension device in the outside of the side wall of the bobbin case. In the shuttle described in Specification 392,947, in the bobbin case is mounted in the shuttle case in a housing concentric with the axis of rotation of the shuttle. This is modified for the purpose of the present invention by mounting the shuttle case 1 eccentric to the axis of the shuttle case. As the setting of the thread lock is being completed the beak 9 of the shuttle is commencing to rise. When the setting is complete, continued rotation of the shuttle case 1, acting through the eccentric pin supporting the bobbin case 3, causes the bobbin case to lift bodily and causes thread to be drawn off the bobbin. As the shuttle beak descends the bobbin case will descend bodily and will slacken the length of shuttle thread. These thread drawing-off and slackening movements of the bobbin case take place during the first half of each stitch-forming cycle, i.e. during the first two rotations of the shuttle. As the shuttle makes its second rotation during the second half of the machine cycle, the shuttle beak 9 engages the loop of needle thread held open for it by the needle 11 and thread lifter 13, as in Specification 410,463, and rises to lift the needle loop over the shuttle. As the shuttle beak rises the bobbin case 3 also rises bodily and draws taut the slackened thread. As the shuttle beak and bobbin case descend in unison towards the work, the loop of needle thread is drawn down towards the work over the shuttle and round the thread issuing therefrom, by the rotary take up of the machine, and the bobbin case will once more rapidly slacken the shuttle thread. The shuttle thread will therefore be in a slackened condition when it is engaged by the loop of needle thread which can pull it towards the work without causing any appreciable reeving. The shuttle is driven by four spring pressed plungers 15, Figs. 5 and 6 in the cam member 17. The ends of the plungers are bevelled to provide wedge shaped ends 19 lying radially of the shaft 27. A ring 21 secured to the upper face of the spiral gear 23 rotating the shuttle shaft has four radial grooves 25 to engage the plungers 15 and couple the gear to the shaft 27. Strong springs 29 maintain the engagement.